The present invention relates to a pressure sensitive adhesive double coated sheet. More particularly, the present invention relates to a pressure sensitive adhesive double coated sheet for use in processing or protecting a brittle work piece temporarily held on a hard plate.
In recent years, the spread of IC cards is being promoted, and accordingly the reduction of the thickness thereof is demanded. Thus, it is now needed to reduce the thickness of semiconductor chips from the conventional about 350 xcexcm to 50-100 xcexcm or less.
It is common practice to grind a wafer back after the formation of a circuit pattern on a wafer surface. The grinding of the wafer back is performed while a pressure sensitive adhesive sheet is stuck to the circuit surface to thereby protect the circuit surface and fix the wafer. Pressure sensitive adhesive sheets comprising a soft substrate coated with a pressure sensitive adhesive are commonly employed in this use. However, in these pressure sensitive adhesive sheets based on a soft substrate, the tension applied at the adhesion is stored as a residual stress. When the wafer has a large diameter or is ground to an extremely small thickness, the residual stress of the pressure sensitive adhesive sheet surpasses the strength of the wafer with the result that the wafer is warped by the force exerted to cancel the residual stress. Further, after the grinding, the brittleness of the wafer, when supported by a soft substrate, has caused wafer breakage during the carrying of the wafer. Therefore, a method comprising fixing the wafer on a hard material such as a quartz plate or an acrylic plate and grinding the wafer is being studied.
In order to cut a hard brittle material such as a printer head, a glass/epoxy base plate, a glass or a ceramic into small chips, the cutting is performed after fixing the hard brittle material on a hard support material. Pressure sensitive adhesive double coated sheets are used for fixing such a cut piece on a hard support material. However, it is extremely difficult to separate the two hard materials mutually stuck with the conventional pressure sensitive adhesive double coated sheet from each other. When a very brittle material such as a wafer is used, it has been unfeasible to be free from damaging thereof.
Therefore, there is a demand for the development of a pressure sensitive adhesive double coated sheet suitable for fixing any of semiconductor wafers and the above-mentioned various cut pieces on a hard material.
Moreover, in the processing of semiconductor wafers, a surface protective sheet and a pressure sensitive adhesive sheet for fixing a wafer are required during the back grinding and the dicing, respectively. This has been burden some from the view point of process control. Further, the brittleness of the wafer has caused wafer breakage during the carrying of the wafer between the above process steps.
Therefore, there is also a demand for the development of a process enabling performing a sequence of process steps including the above wafer back grinding, dicing and carrying in the same configuration, enabling facilitating a process control and enabling preventing wafer breakage.
The present invention has been made in view of the above state of the prior art. The present invention provides a pressure sensitive adhesive double coated sheet which enables efficiently processing a work piece with high precision, in particular a pressure sensitive adhesive double coated sheet suitable to a process capable of producing IC chips of high thickness precision with high yield by reducing warpage and minimizing carrying breakage in the grinding of extremely thin or large diameter silicon wafers and capable of performing back grinding and dicing in the same configuration. It addition, the present invention provides a process of producing semiconductors of high reliability in which use is made of the above pressure sensitive adhesive double coated sheet.
The pressure sensitive adhesive double coated sheet of the present invention comprises a shrink substrate and, superimposed on both sides thereof, pressure sensitive adhesive layers, at least one of the pressure sensitive adhesive layers being composed of an energy radiation curable pressure sensitive adhesive.
In the present invention, it is preferred that both of the pressure sensitive adhesive layers be composed of an energy radiation curable pressure sensitive adhesive. Further, it is preferred that the shrink substrate be furnished with a multiplicity of minute cuts (or notches). The pressure sensitive adhesive double coated sheet of the present invention is preferably used to fix or protect a work piece during processing of the work piece temporarily held on a hard plate.
That is, the pressure sensitive adhesive double coated sheet of the present invention is preferably used in a process comprising the sequence of steps:
sticking a work piece to be processed to one energy radiation curable pressure sensitive adhesive layer of the above pressure sensitive adhesive double coated sheet while sticking the other pressure sensitive adhesive layer to a hard plate so that the work piece is held on the hard plate;
processing the work piece;
irradiating the energy radiation curable pressure sensitive adhesive layer with energy radiation to cure the same and simultaneously shrinking the shrink substrate; and
peeling the processed work piece from the energy radiation curable pressure sensitive adhesive layer having been irradiated and cured.
In the above method of use as well, it is preferred that both of the pressure sensitive adhesive layers are composed of an energy radiation curable pressure sensitive adhesive. Further, it is preferred that the shrink substrate be furnished with a multiplicity of minute cuts.
In the above method of use, it is preferred that the work piece is a semiconductor wafer having its surface furnished with a circuit pattern, and the processing being the grinding of the back of the wafer.
The work piece may be a semiconductor wafer having its surface furnished with a circuit pattern, and the processing being dicing of the wafer into element chips.
Further, the work piece may be a semiconductor wafer having its surface furnished with a circuit pattern, and the processing being the grinding of back of the wafer and dicing of the wafer into element chips, these being performed in arbitrary sequence.
The above pressure sensitive adhesive double coated sheet of the present invention enables temporarily holding various work pieces on a hard plate to thereby effect the fixing and protection thereof during processing. Also, the pressure sensitive adhesive double coated sheet of the present invention enables easily peeling the work pieces from the sheet by simple operation after the performing of desired processing and protection. Therefore, even if the pressure sensitive adhesive double coated sheet is used in the grinding of the back of, for example, an extremely thin or large-diameter semiconductor wafer, the wafer thickness precision can be enhanced and the warpage of the wafer can be reduced thereby. Further, the breakage during wafer carrying can be prevented. Consequently, the pressure sensitive adhesive double coated sheet of the present invention enables production of various electronic components and semiconductor chips with high yield.
Moreover, a sequence of steps including processing and carrying can be performed in the same wafer configuration in the present invention, so that the process control can be facilitated.